1. Field of the Invention
The invention is directed to an imaging medical diagnosis apparatus and to a method for the operation of a magnetic resonance apparatus.
2. Description of the Prior Art
Ultrasound apparatus, X-ray computed tomography and magnetic resonance imaging are utilized as imaging medical diagnosis modalities. Magnetic resonance technology is a known technique for, among other things, acquiring images of the inside of the body of an examination subject. In a magnetic resonance apparatus, rapidly switched gradient fields that are generated by a gradient system are superimposed on a static basic magnetic field that is generated by a basic field magnet system. Further, a magnetic resonance apparatus has a radiofrequency system that emits radiofrequency signals into the examination subject for triggering magnetic resonance signals, and picks up the resulting magnetic resonance signals. Magnetic resonance images are produced on the basis of these signals.
For operation of a magnetic resonance apparatus, time curves for currents in the gradient system, radiofrequency transmission pulses and sampling periods for magnetic resonance signals are matched to one another. This is implemented in a control system of the magnetic resonance apparatus on the basis of a prescribable sequence.
In various areas of employment of an imaging medical diagnosis apparatus, there is a need to repeatedly image the same region of the examination subject in rapid succession and with a high time resolution. In magnetic resonance technology, this is especially true of dynamic perfusion measurements, dynamic angiographies supported by a contrast agent, and dynamic contrast agent studies, for example in mammography. A number of methods are known with which a time resolution that is mainly limited by a maximum speed of the gradient system can be enhanced, particularly given dynamic measurements.
Thus, for example, planar imaging methods can be designed significantly more efficiently when a number of neighboring slices are acquired time-offset instead of acquiring the layers successively. This is especially advantageous given sequences wherein a time span for the excitation, location encoding and magnetic resonance signal detection for a slice is significantly shorter than a repetition time, so that the difference between the repetition time and the time span can be utilized for further layers for implementing excitation, location encoding and magnetic resonance signal detection. Further details about this are described, for example, in the book by H. Morneburg, “Bildgebende Systems für die medizinische Diagnostik”, Publicis MCD Verlag, Erlangen, 1995, pages 544–548.
For example, an echo multiple use technique is known in connection with multi-echo sequences. In one echo train, the data of at least one echo of the same region entered in the edge region of a first raw data matrix as well as the edge region of a second raw data matrix, and only the respective central regions of the matrices are occupied with data from different echoes. Such a multiple use of an echo for the production of two raw data matrices, for example with different contrast properties, enables a time-saving. Further details about this are described, for example, in the above book on pages 549–557.
U.S. Pat. No. 4,327,325 also discloses a method for time-resolved magnetic resonance imaging, wherein signals are acquired by excitation and phase coding of nuclear spins, the signals being entered row-by-row into a raw data matrix divided into individual segments. An image is produced from every completely occupied raw data matrix, with a motion sequence of a number of images being obtained by acquiring a number of raw data matrices at different points in time. Signals of at least one segment are employed for two temporally successive raw data matrices and the measurement time thus can be shortened.
In a method for operating a magnetic resonance apparatus, German OS 199 24 448 discloses, for improved location/tome resolution, dividing the three-dimensional Fourier space in a phase-coding direction of a sequence into annular segments, with the phase encoding steps being defined in terms of the time sequence such that the central segment of the Fourier space is covered more often than outer segments.